How does the AI determine what to target?

[Fafnir13]

They were sending a steady stream of hunters and fauns past my invading force to get at my cities which were rather well defended. I've noticed this happen many times. In my latest game, it was a tad more pronounced as I blocked off the nearest route and was able to divert their troop flow.
So what exactly are they using to determine where to send their troops?

 

[Grey Fox]

Some cities become very juicy targets. Holy cities, Capitals, and cities that used to belong to them get a bonus when it comes to deciding target. After that it's factors like how well defended the city is, and how close it is.

Don't have it all memorized but those are some of the big factors.